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Since the first LC/ ESI-MS experiment of the Nobel prize winner John B. Fenn in 1984, the coupling of liquid chromatographic to mass spectrometric techniques gained a continuous rapid development.
The lecture will give a general survey of different LC separation techniques as size exclusion chromatography (SEC), liquid adsorption chromatography (LAC), liquid chromatography at critical conditions (LCCC) and gradient elution liquid chromatography (GELC) combined with Matrix assisted Laser Desorption Ionization (MALDI) respectively Electrospray Ionization (ESI) Time of Flight (TOF) mass spectrometry.
Often the deficiencies of stand-alone methods can be bridged. LC, blind to structural information needs mass spectrometry as one of the most powerful detectors able to give detailed information on e.g. the repeat units, functionalization or copolymer composition of the chromatographic separated constituents. A separation prior to MS reduces the polydispersity which is one of the reasons for failing of MS. Also problems with different ionization probabilities in complex mixtures can partly be overcame.
On the basis of different examples on- and offline coupling principles will be compared and the pros and cons of both mass spectrometric techniques will be discussed.
Recently, MALDI imaging techniques in coupling with chromatography have become interesting e.g. for visualization of copolymer composition.
Copolymers made of polycarbonate (PC) and polydimethylsiloxane (PDMS) are broadly applied in material science. High impact-stability and transparency are the marks of bisphenol-A polycarbonate. PDMS on the other hand excels in thermal stability, flame resistance and weatherability. Combining those favourable characteristics in a copolymer yields in a ductile but impact-resistant and flame retardant material. In order to understand the synthesis process and to improve the quality and characteristics of a copolymer, knowing its structure is essential. The challenge lies in the variety of heterogeneities like molecular mass-, block-size- and block-distribution.
This study addresses the structural characterization of PC-PDMS-copolymers using different liquid chromatographic techniques, including two dimensional combinations, hyphenated to MALDI-mass spectrometry and FTIR. The large difference in polarities of PC and PDMS is a challenge for liquid chromatography as well as ionization in MALDI. Nevertheless, we were able to differentiate between homopolymer and actual copolymer, clarify the presence of cyclic structures and gain information about the PDMS blocks